Base station and communication control method

ABSTRACT

A target base station according to one embodiment is a target base station to which a user terminal is handed over from a source base station. The target base station includes a controller configured to, when the target base station and a secondary base station perform dual connectivity communication with the user terminal accompanying the handover, notify the secondary base station of identification information related to a serving gateway connected to the target base station.

RELATED APPLICATION

This application is a continuation application of international application PCT/JP2016/061674, filed Apr. 11, 2016, which claims the benefit of U.S. Provisional Application No. 62/148,953 (filed on Apr. 17, 2015), the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a base station and a communication control method in a mobile communication system.

BACKGROUND ART

Dual connectivity communication is specified in 3GPP (3rd Generation Partnership Project) which is a standardization project for mobile communication systems. The dual connectivity communication is a communication mode in which a master cell group (MCG) and a secondary cell group (SCG) are configured to a user terminal in a RRC (Radio Resource Control) connected mode. The MCG is a serving cell group managed by a master base station. The SCG is a serving cell group managed by a secondary base station.

There are also three types of bearers in total of an MCG bearer, an SCG bearer, and a split bearer for a user data transfer method of dual connectivity communication. The MCG bearer is a bearer whose corresponding radio protocol exists only in the master base station and uses only the resources of the master base station. The SCG bearer is a bearer whose corresponding radio protocol exists only in the secondary base station and uses only resources of the secondary base station. The split bearer is a bearer whose corresponding radio protocol exists in both the master base station and the secondary base station and uses the resources of both the master base station and the secondary base station.

SUMMARY

A target base station according to an embodiment is a base station to which a user terminal is handed over from a source base station. The target base station includes a controller configured to, when the target base station and a secondary base station perform dual connectivity communication with the user terminal accompanying the handover, notify the secondary base station of identification information related to a serving gateway connected to the target base station.

A secondary base station according to an embodiment is configured to perform dual connectivity communication with a user terminal together with a target base station in a case where the user terminal is handed over from a source base station. The secondary base station includes a controller configured to perform a process of receiving, from the target base station, identification information related to a serving gateway connected with the target base station.

A communication control method according to an embodiment includes the steps of: handing over a user terminal from a source base station to a target base station; and notifying a secondary base station of identification information from the target base station when the target base station and the secondary base station perform dual connectivity communication with the user terminal accompanying the handover, the identification information being related to a serving gateway connected to the target base station.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a configuration of an LTE system.

FIG. 2 is a protocol stack diagram of a radio interface of the LTE system.

FIG. 3 is a block diagram of a UE (user terminal).

FIG. 4 is a block diagram of an eNB (base station).

FIGS. 5A and 5B are views for explaining an outline of dual connectivity communication according to the embodiment.

FIG. 6 is a view illustrating an example of operation environment according to the embodiment.

FIG. 7 is a view illustrating another example of the operation environment according to the embodiment.

FIG. 8 is a sequence diagram illustrating an example of an operation sequence according to the embodiment.

DESCRIPTION OF EMBODIMENTS Outline of Embodiment

The embodiment assumes dual connectivity communication of an SCG bearer scheme. According to the dual connectivity communication of the SCG bearer scheme, a bearer which does not pass through a master base station is established between a user terminal and a serving gateway. In this case, it is demanded that the serving gateway connected to the master base station and the serving gateway connected to the secondary base station are the same.

For dual connectivity communication of the SCG bearer scheme, it is studied to enable inter master base station handover which changes the master base station without changing the secondary base station. However, according to the inter master base station handover, the serving gateway connected to the master base station may be changed. Consequently, it is concerned that the serving gateways do not match between the master base station and the secondary base station.

The following embodiment discloses a technique which enables smooth dual connectivity communication after the handover.

A target base station according to an embodiment is a base station to which a user terminal is handed over from a source base station. The target base station includes a controller configured to, when the target base station and a secondary base station perform dual connectivity communication with the user terminal accompanying the handover, notify the secondary base station of identification information related to a serving gateway connected to the target base station.

A secondary base station according to an embodiment is configured to perform dual connectivity communication with a user terminal together with a target base station in a case where the user terminal is handed over from a source base station. The secondary base station includes a controller configured to perform a process of receiving, from the target base station, identification information related to a serving gateway connected with the target base station.

A communication control method according to an embodiment includes the steps of: handing over a user terminal from a source base station to a target base station; and notifying a secondary base station of identification information from the target base station when the target base station and the secondary base station perform dual connectivity communication with the user terminal accompanying the handover, the identification information being related to a serving gateway connected to the target base station.

Embodiment (1) Configuration of Mobile Communication System

FIG. 1 is a view illustrating a configuration of an LTE system which is the mobile communication system according to the embodiment. As illustrated in FIG. 1, the LTE system according to the first embodiment includes UEs (User Equipment) 100, an E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) 10 and an EPC (Evolved Packet Core) 20.

Each UE 100 corresponds to a user terminal. The UE 100 is a mobile communication apparatus, and performs radio communication with cells (serving cells). A configuration of each UE 100 will be described below.

The E-UTRAN 10 corresponds to a radio access network. The E-UTRAN 10 includes eNBs 200 (evolved Node-B). Each eNB 200 corresponds to a base station. The eNBs 200 are connected with each other via an X2 interface. A configuration of each eNB 200 will be described below.

The eNB 200 manages one or a plurality of cells, and performs radio communication with the UEs 100 which have established connection with the cell of this eNB 200. The eNB 200 includes a radio resource managing (RRM) function, a user data (simply referred to as “data” below) routing function and a measurement control function for mobility control and scheduling. The “cell” is used not only as a term which indicates a minimum unit of a radio communication area, and but also as a term indicating a function of performing radio communication with the UEs 100.

The EPC 20 corresponds to a core network. The EPC 20 includes MMEs (Mobility Management Entity)/S-GW (Serving-Gateway) 300. The MME corresponds to a mobility management device, and performs various types of mobility control on each UE 100. Each S-GW controls data transfer. Each MME/S-GW 300 is connected with each eNB 200 via an S1 interface. The E-UTRAN 10 and the EPC 20 configure a network.

(2) Configuration of Radio Interface

FIG. 2 is a protocol stack diagram of a radio interface of the LTE system. As illustrated in FIG. 2, a radio interface protocol is partitioned into a first layer to a third layer of an OSI reference model, and the first layer is a physical (PHY) layer. The second layer includes an MAC (Medium Access Control) layer, a RLC (Radio Link Control) layer and a PDCP (Packet Data Convergence Protocol) layer. The third layer includes a RRC (Radio Resource Control) layer.

In the physical layer, encoding, decoding, modulation, demodulation, antenna mapping, antenna demapping, resource mapping and resource demapping are performed. Data and control signals are transmitted between the physical layer of each UE 100 and the physical layer of each eNB 200 via a physical channel.

In the MAC layer, data prioritization control, a retransmission process according to hybrid ARQ (HARQ), and a random access procedure are performed. Data and control signals are transmitted between the MAC layer of each UE 100 and the MAC layer of each eNB 200 via a transport channel. The MAC layer of each eNB 200 includes a scheduler which determines a transport format (a transport block size and a modulating/encoding method (MCS)) in uplink and downlink, and allocated resource blocks for each UE 100.

In the RLC layer, data is transmitted to the RLC layer at a reception side by using functions of the MAC layer and the physical layer. Data and control signals are transmitted between the RLC layer of each UE 100 and the RLC layer of each eNB 200 via a logical channel.

In the PDCP layer, header compression, header extension, encryption and decoding are performed.

The RRC layer is defined only in a control plane which handles a control signal. A message (RRC message) for various configurations is transmitted between the RRC layer of each UE 100 and the RRC layer of each eNB 200. In the RRC layer, a logical channel, a transport channel and a physical channel are controlled in response to establishment, reestablishment and release of a radio bearer. When the RRC of each UE 100 and the RRC of each eNB 200 are connected (RRC connection), each UE 100 is in a RRC connected mode and, when this is not a case, each UE 100 is in a RRC idle mode.

In a NAS (Non-Access Stratum) layer is a higher layer than the RRC layer, session management and mobility management are performed.

(3) Configuration of User Terminal

FIG. 3 is a block diagram of the UE 100 (user terminal). As illustrated in FIG. 3, the UE 100 includes a receiver 110, a transmitter 120, and a controller 130.

The receiver 110 performs various types of reception under control of the controller 130. The receiver 110 includes an antenna and a receiver. Further, the receiver converts a radio signal received at the antenna into a baseband signal (received signal) to output to the controller 130.

The transmitter 120 performs various types of transmission under control of the controller 130. The transmitter 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) outputted from the controller 130 into a radio signal to transmit from the antenna.

The controller 130 performs various types of control in the UE 100. The controller 130 includes a processor and a memory. The memory stores programs executed by the processor and information used for a process performed by the processor. The processor includes a baseband processor which modules, demodulates, encodes and decodes baseband signals, and a CPU (Central Processing Unit) which executes the programs stored in the memory to execute various types of processes. The processor may further include a codec which encodes and decodes audio and video signals. The processor executes the above-described various communication protocols and processes described later.

(4) Configuration of Base Station

FIG. 4 is a block diagram of the eNB 200 (base station). As illustrated in FIG. 4, the eNB 200 includes a transmitter 210, a receiver 220, a controller 230, and a backhaul communication unit 240.

The transmitter 210 performs various types of transmission under control of the controller 230. The transmitter 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) outputted from the controller 230 into a radio signal to transmit from the antenna.

The receiver 220 performs various types of reception under control of the controller 230. The receiver 220 includes an antenna and a receiver. The receiver converts a radio signal received at the antenna into a baseband signal (received signal) to output to the controller 230.

The controller 230 performs various types of control in the eNB 200. The controller 230 includes a processor and a memory. The memory stores programs executed by the processor and information used for a process performed by the processor. The processor includes a baseband processor which modules, demodulates, encodes and decodes baseband signals, and a CPU (Central Processing Unit) which executes the programs stored in the memory to execute various types of processes. The processor executes the above-described various communication protocols and processes described later.

The backhaul communication unit 240 is connected with the neighboring eNBs 200 via an X2 interface, and is connected with the MME/S-GWs 300 via the S1 interface. The backhaul communication unit 240 is used for communication performed on the X2 interface, and communication performed on the S1 interface.

(5) Outline of Dual Connectivity Communication

The dual connectivity communication is a communication mode in which a master cell group (MCG) and a secondary cell group (SCG) are configured in the UE 100 in the RRC connected mode. The MCG is a serving cell group managed by a master base station (MeNB). The SCG is a serving cell group managed by a secondary base station (SeNB). Radio resources are allocated to the UE 100 from each eNB 200, so that improvement of throughput is expected.

In dual connectivity communication, among a plurality of eNBs 200 which establishes connection with the UE 100, only the MeNB 200M establishes RRC connection with the UE 100. In contrast, an SeNB 200S provides additional radio resources to the UE 100 without establishing RRC connection with the UE 100. There is the X2 interface between an MeNB 200M and the SeNB 200S.

FIGS. 5A and 5B are views for explaining an outline of dual connectivity communication according to the embodiment. The embodiment assumes the dual connectivity communication of the SCG bearer scheme (SCG bearer option). FIGS. 5A and 5B illustrate a downlink data path. However, an uplink data path is also configured similar to the downlink.

As illustrated in FIG. 5A, the UE 100 includes two bearers (an EPS bearer #1 and an EPS bearer #2). The EPS bearer #1 is a bearer which passes through an S-GW 300U and the MeNB 200M. Such a bearer will be referred to as an MCG bearer. The EPS bearer #2 is a bearer which passes through the S-GW 300U and the SeNB 200S. Such a bearer will be referred to as an SCG bearer.

The S-GW 300U sorts the two bearers of the UE 100 to the MeNB 200M and the SeNB 200S. Therefore, it is demanded that an S-GW having a data path (S1 bearer) to the MeNB 200M, and an S-GW having a data path (S1 bearer) to the SeNB 200S are the same.

As illustrated in FIG. 5B, the MeNB 200M processes data belonging to the EPS bearer #1 in each layer of PDCP, RLC, and MAC. The SeNB 200S processes data belonging to the EPS bearer #2 in each layer of PDCP, RLC, and MAC.

(6) Operation Environment According to Embodiment

The embodiment assumes that inter MeNB handover (inter MeNB handover without SeNB change) which changes the MeNB 200M without changing the SeNB 200S is performed for the dual connectivity communication of the SCG bearer scheme.

FIG. 6 is a view illustrating an example of the operation environment according to the embodiment.

As illustrated in FIG. 6, the secondary base station (SeNB 200S) is located near a boundary of a coverage of the source base station (S-MeNB 200M1) and a coverage of a target base station (T-MeNB 200M2). FIG. 6 illustrates an example where the S-MeNB 200M1 and the T-MeNB 200M2 are macrocell base stations and the SeNB 200S is a small cell base station.

The S-MeNB 200M1, the T-MeNB 200M2, and the SeNB 200S are connected with each other via the X2 interface. In addition, each of the S-MeNB 200M1, the T-MeNB 200M2, and the SeNB 200S is connected to the same S-GW 300U via an S1-U interface (S1 bearer). The S-MeNB 200M1 and the T-MeNB 200M2 are connected to the same MME (not illustrated) via an S1-MME interface.

In such operation environment, the UE 100 first performs dual connectivity communication with the S-MeNB 200M1 and the SeNB 200S at a point A in the coverage of the SeNB 200S. Next, the UE 100 moves toward a point B in the coverage of the SeNB 200S and is handed over from the S-MeNB 200M1 to the T-MeNB 200M2. The UE 100 performs dual connectivity communication with the T-MeNB 200M2 and the SeNB 200S without changing the SeNB 200S at point B.

FIG. 7 is a view illustrating another example of the operation environment according to the embodiment.

As illustrated in FIG. 7, the S-MeNB 200M1 and the T-MeNB 200M2 are connected to different S-GWs. More specifically, the S-MeNB 200M1 is connected with an S-GW 300U1 via the S1-U interface (S1 bearer), and the T-MeNB 200M2 is connected with an S-GW 300U2 via the S1-U interface (S1 bearer). The S-MeNB 200M1 and the T-MeNB 200M2 are connected to the same MME (not illustrated) via the S1-MME interface.

In such operation environment, when the UE 100 is handed over similar to the above, relocation of the S-GWs (S-GW relocation) occurs before and after the handover. As a result, the S-GWs do not match between the T-MeNB 200M2 and the SeNB 200S. In this case, when the SeNB 200S cannot acquire information (identification information) related to the new S-GW 300U2, it is not possible to appropriately perform dual connectivity communication.

In the embodiment, when the T-MeNB 200M2 and the SeNB 200S perform the dual connectivity communication with the UE 100 accompanying the handover, the T-MeNB 200M2 notifies the SeNB 200S of the identification information related to the S-GW 300U2 connected to the T-MeNB 200M2. The identification information related to the S-GW 300U2 includes at least one of an “E-RAB (E-UTRAN Radio Access Bearer) ID”, a “Transport Layer Address”, and a “GTP-TEID (GPRS Tunneling Protocol-Tunnel Endpoint Identifier)”. Consequently, it is possible to smoothly perform dual connectivity communication after the handover.

(7) Identification Information Related to Serving Gateway

Hereinafter, the identification information related to the S-GW 300U2 (serving gateway) will be described in detail.

The “E-RAB ID” is an ID for identifying an E-RAB.

The “Transport Layer Address” is an IP address of the S-GW. This information makes it possible to grasp which S-GW to connect. When the S-GW is changed, this IP address will be naturally changed, too. In the future, it is also possible to assume a flow that the S-GW is virtualized and plays a role of a plurality of S-GWs in one server. In such a case, there is a possibility that the IP address is not changed even when the S-GW is changed, so that a next GTP-TEID can be used.

The “GTP-TEID” indicates the GTP-TEID of the S1-U, and, more specifically, is an ID assigned to both ends of the S1 bearer (S1 transport bearer). That is, the “GTP-TEID” is assigned to both ends (an eNB side and an S-GW side) of one S1-U bearer. When the eNB knows the ID of the S-GW side, the UL data transmission destination can be identified, and when the S-GW knows the ID assigned by the eNB, the DL data transmission destination can be identified. Each ID is allocated as an address of a data transmission destination of each data transmission destination node.

(8) Operation Sequence According to Embodiment

FIG. 8 is a sequence diagram illustrating an example of an operation sequence according to the embodiment. Hereinafter, a handover sequence in the operation environment illustrated in FIG. 7 will be described. In the initial state of FIG. 8, the UE 100 performs dual connectivity communication with the S-MeNB 200M1 and the SeNB 200S.

As illustrated in FIG. 8, in step 1, the S-MeNB 200M1 transmits a handover request (Handover Request) message for requesting the handover of the UE 100 to the T-MeNB 200M2. The “Handover Request” includes identification information related to the S-GW 300U1 connected to the S-MeNB 200M1. The identification information related to the S-GW 300U1 includes at least one of the “E-RAB ID”, the “Transport Layer Address” and the “GTP-TEID”. Further, the “Handover Request” may include identification information related to the SeNB 200S. The identification information related to the SeNB 200S includes an eNB ID (Global eNB ID). Further, the identification information related to the SeNB 200S may include at least one of the “E-RAB ID”, the “Transport Layer Address” and the “GTP-TEID” as information of bearers established for the SeNB 200S.

In step 2, in response to reception of the “Handover Request” message, the T-MeNB 200M2 transmits an addition request (SeNB Addition Request) message for requesting addition of the SeNB 200S to the SeNB 200S.

In step 3, in response to the reception of the “SeNB Addition Request” message, the SeNB 200S transmits an “SeNB Addition Request Ack” message to the T-MeNB 200M2. The “SeNB Addition Request Ack” message includes SCG configuration information.

In step 4, the T-MeNB 200M2 transmits a handover acknowledgment response (Handover Request Ack) message to the “Handover Request” message to the S-MeNB 200M1. The “Handover Request Ack” message includes MCG configuration information and SCG configuration information.

In step 5, the S-MeNB 200M1 transmits an SeNB release request (“SeNB Release Request) message to the SeNB 200S.

In step 6, in response to reception of the “Handover Request Ack” message, the S-MeNB 200M1 transmits a RRC connection reconfiguration (RRC Connection Reconfiguration) message to the UE 100. The “RRC Connection Reconfiguration” message corresponds to a handover command for instructing handover to the T-MeNB 200M2, and includes the SCG configuration information and the MCG configuration information.

In step 7, in response to reception of the “RRC Connection Reconfiguration” message, the UE 100 performs a random access procedure (Random Access Procedure) on the T-MeNB 200M2.

In step 8, the UE 100 transmits a RRC connection reconfiguration complete (RRC Connection Reconfiguration Complete) message to the T-MeNB 200M2.

In step 9, the UE 100 performs the “Random Access Procedure” on the SeNB 200S. However, instead of the “Random Access Procedure”, RRC connection re-establishment (RRC Connection Re-establishment) may be performed on the SeNB 200S.

In step 10, the T-MeNB 200M2 transmits an SeNB reconfiguration complete (SeNB Reconfiguration Complete) message to the SeNB 200S.

In step 11, the S-MeNB 200M1 transmits an “SN Status Transfer” to the T-MeNB 200M2.

In step 12, the S-MeNB 200M1 performs “Data Forwarding” of forwarding data received from the S-GW 300U1 to the T-MeNB 200M2.

In step 13, the T-MeNB 200M2 transmits a data path switch request (Path Switch Request) message to an MME 300C.

In step 14, in response to reception of the “Path Switch Request” message, the MME 300C transmits a create session request (Create Session Request) message to the S-GW 300U2.

In step 15, the S-GW 300U2 transmits a response (Response) to the “Create Session Request” message to the MME 300C.

In step 16, in response to reception of a response (Response) from the S-GW 300U2, the MME 300C transmits a path switch response (Path Switch Request Acknowledge) message indicating the data path switch from the S-MeNB 200M1 to the T-MeNB 200M2 to the T-MeNB 200M2. The “Path Switch Request Acknowledge” message includes identification information related to the S-GW 300U2. As described above, the identification information related to the S-GW 300U2 includes at least one of the “E-RAB ID”, the “Transport Layer Address” and the “GTP-TEID”. The “E-RAB ID”, the “Transport Layer Address” and the “GTP-TEID” are included in “E-RABs Switched in Uplink Item IEs” in the “Path Switch Request Acknowledge” message.

In step 17, the T-MeNB 200M2 compares the “Transport Layer Address” in the “Handover Request” message and the “Transport Layer Address” in the “Path Switch Request Acknowledge” message. The “Transport Layer Address” in the “Handover Request” message corresponds to the address information of the S-GW 300U1. The “Transport Layer Address” in the “Path Switch Request Acknowledge” message corresponds to the address information of the S-GW 300U2.

In addition, the T-MeNB 200M2 may compare the “GTP-TEID” (the “GTP-TEID” related to the S-GW 300U1) in the “Handover Request” message and the “GTP-TEID” (the “GTP-TEID” related to the S-GW 300U2) in the “Path Switch Request Acknowledge” message. In addition, the T-MeNB 200M2 may compare the “E-RAB ID” (the “E-RAB ID” related to the S-GW 300U1) in the “Handover Request” message and the “E-RAB ID” (the “E-RAB ID” related to the S-GW 300U2) in the “Path Switch Request Acknowledge” message.

When the match is not found as a result of the comparison, the T-MeNB 200M2 notifies the SeNB 200S of the identification information related to the S-GW 300U2. The identification information related to the S-GW 300U2 includes at least one of the “E-RAB ID”, the “Transport Layer Address” and the “GTP-TEID”. When making comparison with the “Transport Layer Address”, the T-MeNB 200M2 preferably notifies the SeNB 200S of the “Transport Layer Address”. Also, when making comparison with the “GTP-TEID”, the T-MeNB 200M2 preferably notifies the SeNB 200S of the “GTP-TEID”. In this regard, the T-MeNB 200M2 may make comparison with the “Transport Layer Address” and comparison with the “GTP-TEID”. Further, the T-MeNB 200M2 may notify both of the “Transport Layer Address” and the “GTP-TEID”.

The SeNB 200S performs a process of receiving the identification information related to the S-GW 300U2 from the T-MeNB 200M2. Then, the SeNB 200S may establish a data path to the S-GW 300U2 based on the identification information related to the S-GW 300U2. The SeNB 200S may establish the data path to the S-GW 300U2 by switching to the S-GW 300U2 a path to the S-GW 300U1. Alternatively, the SeNB 200S may store the identification information related to the S-GW 300U2 as the context information of the UE 100.

In step 18, the T-MeNB 200M2 transmits a “UE Context Release” message indicating release of UE context information to the S-MeNB 200M1. In this regard, the process in step 18 may be performed before notification of the identification information related to the S-GW 300U2.

In step 19, in response to the reception of the “UE Context Release” message, the S-MeNB 200M1 transmits a “UE Context Release” message to the SeNB 200S.

Although the embodiment including step 1 to step 19 has been described. However, the present disclosure is not limited to this, and part of steps may be omitted.

(9) Summary of Embodiment

When the T-MeNB 200M2 according to the embodiment and the SeNB 200S perform the dual connectivity communication with the UE 100 accompanying the handover of the UE 100, the T-MeNB 200M2 notifies the SeNB 200S of the identification information related to the S-GW 300U2 connected to the T-MeNB 200M2. As a result, it is possible to smoothly perform dual connectivity communication after the handover.

Modified Example of Embodiment

In the above embodiment, when deciding that an S-GW (S-GW 300U2) connected to a T-MeNB 200M2 is different from an S-GW (S-GW 300U1) connected to an S-MeNB 200M1, the T-MeNB 200M2 notifies the SeNB 200S of identification information related to the S-GW 300U2.

However, irrespectively of whether or not the S-GW connected to the T-MeNB 200M2 is different from the S-GW connected to the S-MeNB 200M1, the T-MeNB 200M2 may notify the SeNB 200S of the identification information related to the S-GW 300U2 notified from the MME 300C. In this case, the T-MeNB 200M2 may notify the SeNB 200S of information indicating the decision result as to whether or not the S-GW connected to the T-MeNB 200M2 is different from the S-GW connected to the S-MeNB 200M1 together with the identification information. Also, the T-MeNB 200M2 may omit the decision on whether or not the S-GW connected to the T-MeNB 200M2 is different from the S-GW connected to the S-MeNB 200M1, and notify of the identification information related to the S-GW 300U2 notified from the MME 300C. In that case, the SeNB 200S may decide whether or not the identification information related to the S-GW 300U2 notified from the MME 300C the identification information related to the S-GW 300U1 match.

Other Embodiments

The above embodiment assumes inter master base station handover which changes a master base station from an S-MeNB 200M1 to a T-MeNB 200M2 without changing an SeNB 200S. However, instead of the inter master base station handover, the present disclosure may be applied to “Handover with SeNB Addition”. The “Handover with SeNB Addition” is a method for starting dual connectivity communication during handover although the dual connectivity communication is not performed before the handover. In the case of the “Handover with SeNB Addition”, step 5 and step 18 illustrated in FIG. 8 are unnecessary.

In the above embodiment, an LTE system has been exemplified as a mobile communication system. However, the present disclosure is not limited to the LTE system. The present disclosure may be applied to systems other than the LTE system.

The above-described embodiment assumes that the SeNB 200S is not changed during the inter master base station handover. However, the present disclosure is not limited to this. For example, the embodiment may include that the SeNB 200S (SeNB 200S1) is changed to the another SeNB 200S (SeNB 200S2). 

1. A target base station to which a user terminal is handed over from a source base station, the target base station comprising a controller configured to, when the target base station and a secondary base station perform dual connectivity communication with the user terminal accompanying the handover, notify the secondary base station of identification information related to a serving gateway connected to the target base station.
 2. The target base station according to claim 1, wherein the controller is configured to perform a process of receiving a path switch response message from a mobility management device, the path switch response message indicating a data path switch from the source base station to the target base station, the path switch response message includes the identification information, and the controller is configured to notify the secondary base station of the identification information included in the path switch response message.
 3. The target base station according to claim 1, wherein the identification information includes at least one of an “E-RAB (Evolved-universal mobile telecommunications system terrestrial radio access network radio access bearer) ID”, a “Transport Layer Address”, and a “General packet radio service tunneling protocol-tunnel endpoint identifier (GTP-TEID)”.
 4. The target base station according to claim 1, wherein the controller is configured to, when deciding that the serving gateway connected with the target base station and a serving gateway connected to the source base station are different, notify the secondary base station of the identification information.
 5. The target base station according to claim 1, wherein the controller is configured to notify the secondary base station of information together with the identification information, the information indicating a decision result as to whether or not the serving gateway connected to the target base station is different from a serving gateway connected to the source base station.
 6. The target base station according to claim 1, wherein dual connectivity communication is dual connectivity communication of an SCG (Secondary Cell Group) bearer scheme configured to establish a bearer between the user terminal and the serving gateway without passing through the target base station.
 7. The target base station according to claim 1, wherein the handover is inter master base station handover configured to change a master base station from the source base station to the target base station without changing the secondary base station.
 8. A secondary base station configured to perform dual connectivity communication with a user terminal together with a target base station in a case where the user terminal is handed over from a source base station, the secondary base station comprising: a controller configured to perform a process of receiving, from the target base station, identification information related to a serving gateway connected with the target base station.
 9. The secondary base station according to claim 8, wherein the controller is configured to perform, based on the identification information, at least one of a process of establishing a data path to the serving gateway, a process of switching a data path from a serving gateway connected to the source base station to the serving gateway connected to the target base station, and a process of saving the identification information as context information of the user terminal.
 10. The secondary base station according to claim 8, wherein the identification information includes at least one of an “E-RAB (Evolved-universal mobile telecommunications system terrestrial radio access network radio access bearer) ID”, a “Transport Layer Address”, and a “General packet radio service tunneling protocol-tunnel endpoint identifier (GTP-TEID).
 11. The secondary base station according to claim 8, wherein the identification information is notified from the target base station when the target base station decides that the serving gateway connected to the target base station is different from a serving gateway connected to the source base station.
 12. The secondary base station according to claim 8, wherein the controller is configured to perform a process of receiving information together with the identification information from the target base station, the information indicating a decision result as to whether or not a serving gateway connected to the source base station and the serving gateway connected to the target base station are different.
 13. The secondary base station according to claim 8, wherein the dual connectivity communication is dual connectivity communication of an SCG (Secondary Cell Group) bearer scheme configured to establish a bearer between the user terminal and the serving gateway without passing through the target base station.
 14. The secondary base station according to claim 8, wherein the handover is inter master base station handover configured to change a master base station from the source base station to the target base station without changing the secondary base station.
 15. A communication control method comprising the steps of: handing over a user terminal from a source base station to a target base station; and notifying a secondary base station of identification information from the target base station when the target base station and the secondary base station perform dual connectivity communication with the user terminal accompanying the handover, the identification information being related to a serving gateway connected to the target base station. 